Haddon — On Generative and Urinary Ducts in Chitons. 227 



may be compared with a byssus organ of very primitive construc- 

 tion, or may prove to play some accessory function subordinate to 

 the secretion of generative materials. 



The same organ, although in a much less developed condition, 

 was found by Hubrecht in Neomenia; the muscles, too, are nothing 

 like so well developed as in the former genus. 



It is possible that these glands of the Neomenise may be homo- 

 logous with the glands in question. The difference in position need 

 prove no difficulty, since it would be only another example of the 

 tendency of certain terminal organs in the Amphineura (such as the 

 branchise, excretory, and generative ducts) to extend along each 

 side of the body. A greater difficulty exists in a comparison of the 

 structure of the glands themselves ; but this I will leave for the 

 present, till I am able to state how they occur in other species of 

 Chitons. 



Midneys and their Ducts. — Until Sedgwick's investi- 

 gation in 1881 (8), our knowledge of the structure and relations of 

 the kidneys of the Chitons was of the most unsatisfactory and con- 

 tradictory kind possible. 



Middendorff (2) figures and thus describes, in Ch. steUeri, a 

 gland which he identified as the kidney : — " To the naked eye it 

 appears as a very broad velvet-like covering on the shining tendon- 

 mass of the ventral muscles ; the middle area only of the ventral 

 body- wall is left free ; the sides of it, however, and a portion of the 

 lateral wall of the body-cavity are covered in the form of a horse- 

 shoe ; each limb of this horse-shoe arises close behind the anterior 

 diaphragm, proceeds backwards, and unites with its fellow in a 

 closed arch on the front wall of the posterior diaphragm." The 

 gland itself is stated to consist of a longitudinal canal beset with 

 ramified cseca. The whole structure is very delicate, and possesses 

 extremely thin walls. The Russian naturalist gives no account of 

 the histology of the gland, and is careful to add that he was 

 unable to discover its external opening or its relation to the other 

 viscera. 



Schiff (3) could not find this gland in Ch. piceus, and throws 

 doubt upon Middendorff 's interpretation.^ 



^ I have roughly dissected a Ch. piceus from the Barbadoes, and have seen the 

 kidney, but I have not j^i made out its relations. — A. C. H. 



